Relief of pain. Opiates alter the perception 
or appreciation of pain and are effective in 
controlling `deep' visceral (internal) pain. 
Non-opiates, such as aspirin, paracetamol, 
and NSAIDs, relieve musculoskeletal pain and 
reduce inflammation in soft tissues. Pain is 
the sensation that is felt when electrical 
stimuli travel along a nerve pathway, from 
peripheral nerve fibres to the brain via the 
spinal cord. An anaesthetic agent acts either 
by preventing stimuli from being sent 
(local), or by removing awareness of them 
(general). Analgesic drugs act on the central 
nervous system. Severe or chronic pain cannot 
be controlled by drugs. Temporary or 
permanent analgesia is achieved by injection 
of an anaesthetic agent into, or the severing 
of, a nerve. Implanted devices enable 
patients to deliver controlled electrical 
stimulation to block pain impulses. 
Production of the body's natural opiates, 
endorphins, can be manipulated by techniques 
such as relaxation and biofeedback.